This invention is primarily concerned with the connection of multimode fibres of core diameter typically of 50-200.mu. which when the cladding is taken into account is 125-400.mu.. The optical fibres with their so-called buffer or insulating coating have a diameter of up to 1 mm. In the case of polymer clad fibres the diameter may range from 0.5 mm to 1.5 mm. The buffer or secondary coated fibres may be as such or they may be in the form of a so-called ruggedized fibre in which the core is loose in a jacket or is tightly held in the jacket by an intervening layer, e.g. of polyimide ("Kevlar") fibres.
A problem that has existed in the termination of such fibres by means of a connector tip or ferrule has been to avoid the need to fix the fibre into the ferrule by means of an adhesive and then to polish the ferrule. U.S. Pat. No. 4,368,948 (Despouys) teaches the removal of the buffer coating along a predetermined length from one end of the fibre followed by threading the fibre through a connector tip so that a portion of the fibre stripped of its outside sheath is within the connector tip and the remaining stripped portion of the fibre projects from the front end of the connector tip. The connector tip is joined to a portion of the fibre tip still bearing its buffer coating by crimping and a portion of the fibre stripped of its outside sheath and projecting through a spot face of the ferrule at the front end of the counterbore is severed inwardly of the front face of the fibre to provide an optical end face. But we have found that it is difficult to get reliable results by crimping onto the buffer layer because there is a risk of damaging the fibre and creating sources of optical loss. A tool having special crimping jaws set to the size of the fibre is required which increases the equipment to be taken into the field. Furthermore, the connector tip is single use and does not allow repeated terminations to be made reusing the same components.
The use of slotted insert within a crimping ring axially to locate the buffer material of an optical fibre is described in U.S. Pat. No. 4,447,121 (Cooper et al) and the use of a helically slotted conical clamping member to hold and axially locate an optical fibre after its buffer layer has been removed is described in our G.B. Pat. No. 2040062.